In general, PC motherboards are provided with a video card receiving slot for receiving a video card. Originally, one type of video card was provided, and this required that a 3.3 volt supply should be applied to the terminating resistors of the AGP bus on the PC motherboard. However, more recently a second type of video card has been introduced which will operate in the same video card receiving slot but requires that a regulated 1.5 volt supply should be provided to the terminating resistors of the AGP bus on the PC motherboard, In general, a sensor is provided in the video card receiving slot for detecting the type of video card inserted in the slot. This sensor outputs a signal which, in general, is referred to as a TYPEDET signal which, when it is at zero volts indicates that a video card requiring the regulated 1.5 volt supply has been inserted in the video card slot, and when the TYPEDET signal is floating, a 3.3 volt supply is required. A control circuit is therefore required for decoding the TYPEDET signal and for selecting an output voltage at the two respective levels of 1.5 volts regulated and 3.3 volts from a voltage source for applying to the terminating resistors of the AGP bus in response to the TYPEDET signal. It is preferable that such a control circuit should be adapted to isolate the AGP bus from the voltage source during power up to avoid power up sequencing problems. A further requirement of such a control circuit may be that in the event of a control terminal of the control circuit being isolated from the TYPEDET signal and remaining unconnected to any signal, in other words, being in a floating state, the voltage applied to the terminating resistors of the AGP bus should also be 1.5 volts regulated. It is important that any such control circuit for controlling the voltage to the terminating resistors of the AGP bus in response to the various inputs should have the minimum number of terminals so that the circuit can be implemented in the form of an IC chip with the minimum number of pins. Ideally, the number of pins should not exceed five.